Roller vane pump incorporating a bearing bush

ABSTRACT

Roller vane pump, in particular suited for pumping fluid in a continuously variable automatic transmission of a motor vehicle, provided with a pump housing accommodating a substantially cylindrical carrier, which is rotatable about a central axis, and a cam ring encompassing the carrier in the radial direction, whereby a radial clearance between the carrier and the cam ring varies along a circumference of the carrier, and with a pump shaft extending co-axial with said central axis through the carrier, characterised in that there is provided in the pump housing a bearing bush having an essentially cylindrical central bore through which the pump shaft extends.

BACKGROUND OF THE INVENTION

The invention relates to a roller vane pump and in particular to aroller vane pump suited for pumping fluid in a continuously variableautomatic transmission (CVT) for motor vehicles. Such a roller vane pumpis known from the European patent 0.921.314 and is intended for pumpingautomatic transmission fluid in hydraulically controlled and/or operatedcontinuously variable transmissions for motor vehicles. Particularly ina belt-and-pulley type CVT, a large flow of fluid at a high pressure maybe required for control of the transmission. The known pump may beprovided with several pump units, whereby a pump unit is a functionalpump unit, i.e. having a suction section where fluid is drawn into thepump and a discharge section where fluid is discharged from the pump.Since the pump is usually driven by a main drive shaft of the vehicle,it is designed to be able to provide a desired pump yield, i.e. adesired flow of fluid, even at a lower most rotational speed of thedrive shaft, e.g. idle speed. At the same time, the pump is designed toreliably withstand prolonged operation at an upper most rotational speedof the drive shaft.

The known pump is provided with a pump housing accommodating asubstantially cylindrical carrier, which is rotatable about a centralaxis, and with a cam ring encompassing the carrier in the direction,whereby a clearance in the radial direction between the carrier and thecam ring varies along a circumference of the cam ring. The carrier isprovided with a number of slots extending inwardly from the radiallyouter surface of the carrier, at least some of which slideablyaccommodate a roller element. The carrier is rotatable by means of apump shaft extending co-axial with said central axis through thecarrier. The pump shaft is supported in the housing on axial sides ofthe carrier, whereby the housing provides a bearing surface for the pumpshaft. A small gap exists between the carrier and the pump housing as aresult of an axial clearance introduced there between, which gap allowsthe carrier to rotate with respect to the housing. The gap furtherenables a lubrication flow from the discharge section of a pump unit tothe bearing surface for lubrication thereof. It is noted that, as aconsequence, the gap also enables a leakage flow from the high-pressuredischarge section to the low-pressure suction section, which affectspump efficiency. Usually, said axial clearance will, therefore, be setas little as possible given a desired amount of lubrication.

The known pump has the disadvantage that the carrier may slightly tiltwith respect to the pump housing under the influence of for instancemechanical shocks, changes in the rotational speed or changes in thefluid pressure at the discharge section. Particularly, when the pumpshaft is relatively long a substantial movement of the carrier mayoccur. A rotation of the carrier causes said gap to vary along itscircumference. At a location where said clearance is large, said leakageflow will also be large, whereby the -volumetric- pump efficiency isdisadvantageously affected, whereas at a location where said clearanceis small, possibly even non-existent, friction between the carrier andthe housing is high, whereby the -mechanical- pump efficiency is againdisadvantageously affected. At a location where said gap isnon-existent, wear of the pump housing and of the carrier may alsobecome a problem.

The above mentioned disadvantage of the known pump is particularlyrelevant when the pump housing is made of a light weight and/or softmaterial, such as aluminium, which is generally also a ductile materialand/or when the carrier is rigidly fixed to the pump shaft. In suchcases, said movement of the carrier may occur with relative ease,causing the width of said gap to change considerably along thecircumference of the carrier. It is an object of the present inventionto improve the pump efficiency of the known roller vane pump.

SUMMARY OF THE INVENTION

According to the invention this object is achieved with the roller vanepump, wherein there is provided in the pump housing a bearing bushhaving an essentially cylindrical central bore through which the pumpshaft extends. In the pump according to the invention there is provideda separate bearing bush, which bearing bush accommodates the pump shaftin the pump housing and provides a bearing surface for the rotation ofthe said shaft. The provision of the bearing bush stiffens theconstruction of the pump shaft and thereby reduces said movement of thepump shaft.

In a further development of the invention, the bearing bush is made ofmaterial a less ductile than aluminium, such as copper. It is furtherpreferred that the bearing bush tightly fits around said pump shaft inthe radial direction. Both features have the advantage that the freedomof movement of the pump shaft is restricted. It may also be advantageousto provide a bearing bush on either axial end of the carrier. In thismanner a stable configuration of the pump housing, the pump shaft andthe carrier is achieved.

According to the invention it is advantageous, if the bearing bush isprovided with a lubrication groove on a radially inner surface thereof,preferably having a substantially elongated shape with a long axis, forallowing a fluid to penetrate between the bearing bush and the pumpshaft. To this end the lubrication groove may start at an axial end ofthe bearing bush closest to the carrier and continues with its long axisoriented in a direction having an axial component. The lubricationgroove allows a flow of lubrication fluid in between the pump shaft andthe bearing bush, even if the bearing bush fits relatively tightlyaround said shaft. The lubrication groove may span the entire axiallength of the bearing bush. However, to prevent substantial fluidcommunication with the environment, it is preferred that the lubricationgroove ends at some distance from the axial end of the bearing bushopposite said axial end of the bearing bush closest to the carrier. Whenthe lubrication groove is oriented at an angle with respect to the axialdirection, the lubrication fluid is distributed over at least a part ofa circumference of the pump shaft. For optimum distribution of thelubrication fluid, the said angle is set such that the lubricationgroove extends in the direction of rotation of the pump shaft.

As mentioned in the above, the pump is provided with one or more lowpressure suction sections and one or more high pressure dischargesections, which sections are located alternately along the circumferenceof the cam ring. When said pressures are unevenly distributed along saidcircumference, a net-force acts on the carrier and on the pump shaft ata specific tangential location, which net-force urges the pump shaft ina generally radial direction. Thus, when the pump is provided with asingle pump unit, or when the pump units have mutually differentdischarge pressures, a contact pressure between the pump shaft and thebearing bush is unevenly distributed in dependence on tangentialposition and varies between a highest level, at a tangential positionsubstantially opposite a tangential position of the discharge sectionhaving the highest discharge pressure, and a lowest level, at atangential position substantially corresponding to the tangentialposition of the discharge section having the highest discharge pressure.According to the invention, it is in such cases to be preferred that thelubrication groove is predominantly located in a region of tangentialpositions where the said contact pressure is relatively low, so thatthere is no need to disturb the contact between the pump shaft and thebearing bush at the location where the said contact pressure is thehighest.

In a further elaboration of such embodiment, the lubrication groovestarts at a tangential position of the discharge section where theprevailing pressure is at a maximum, whereby a tangential positioncorresponding to a central part of the said section is particularlysuitable. If in such a case the long axis of the lubrication groove isoriented at an angle with respect to the axial direction, it ispreferable that either one or both of a length of the lubrication grooveand of said angle are chosen such that it extends in the tangentialdirection over an angle which approximately corresponds to π minus ½πdivided the number of pump units of the pump. This measure effects thatthe lubrication groove does not extend into the region of tangentialpositions where the said contact pressure is the highest.

In yet a further development of the pump according to the invention, thebearing bush is provided with a distribution groove on its inner surfacehaving a substantially elongated shape with a long axis that is orientedsubstantially axially and that intersects the long axis of thelubrication groove, for further improving the distribution of thelubrication fluid. The distribution groove may extend over a substantialpart of an axial dimension of the bearing bush. It is, however, to bepreferred if there remains a distance of at least ¼ of the said axialdimension between an axial end of the bearing bush and of thedistribution groove so as to limit communication of lubrication fluidbetween the distribution groove and the environment.

The invention will now be explained in greater detail with reference tothe non-restricting examples of embodiment shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an axial cross section of the known roller vane known pumptaken at an axial position immediately adjacent to the carrier;

FIG. 2 is a tangential cross section of the known pump;

FIG. 3 is a tangential cross section of a roller vane pump according tothe invention;

FIG. 4 is a perspective view of a bearing bush for the roller vane pumpaccording to the invention;

FIG. 5 is a plane view of the inner surface of a bearing bush accordingto the invention.

FIG. 6 illustrates the present invention provided with an input shaft tobe drivably connected to an engine, an output shaft to be drivinglyconnected to a load and provided with a roller vane pump, wherein thepump shaft is drivably connected to the engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 respectively provide an axial cross section and atangential cross section of the known roller vane pump. The known pumpcomprises a pump housing 12 that is composed of three pump housing parts1, 8 and 9, which can be secured to each other by means of bolts (e.g.bolt 25 shown in FIG. 3) that are inserted in holes in the pump housing12, e.g. hole 10. The central pump housing part 1 accommodates anessentially cylindrically shaped carrier 4, which is rotatable about acentral axis 4 a in a direction of rotation indicated by the arrow bymeans of a pump shaft 5, and a cam ring 2 with a radially inwardoriented cam surface 2 a, which cam ring 2 radially encompasses thecarrier 4, whereby a clearance C in the radial direction between thecarrier 4 and the cam ring 2 varies along the circumference of the camring 2. On its periphery the carrier 4 is provided with radiallyinwardly extending slots 6 that accommodate essentially cylindricallyshaped roller elements 7. The roller elements 7 are accommodated in theslots 6, such that they are able to slide in a predominantly radiallyoriented direction. The pump shaft 5 extends in axial direction throughthe carrier 4 and, on either axial side thereof, is supported in thepump housing 12, whereby the housing 12 provides a bearing surface. Thepump shaft 5 is fixed to the carrier 4 by means of a wedge 3.

During operation of the pump, the carrier 4, the cam ring 2, and theroller elements 7 define a number of pump chambers 13 that are bound inaxial sense by the inner surfaces 23 and 14 of the outer pump housingparts 8 and 9 respectively and that may arrive in communication with asupply line 24 in the pump housing 12 for hydraulic fluid, through oneor more of a number of supply ports 11 and 16 and which may arrive incommunication with a discharge line (not shown) in the pump housing 12for hydraulic fluid, through one or more of a number of discharge ports17 and 18. When the carrier 4 is rotated during operation of the pump, asurface area of the pump chambers 13 as seen in axial cyclicallyincrease and decrease, as can be deduced from in FIG. 1. Accordingly, avolume of the pump chambers 13 also cyclically increase and decrease, sothat, on the one hand, fluid sucked from the supply line into the pumpchamber 13 when its volume increases, i.e. at the location of aso-called low pressure pump section L, and, on the other hand, fluid ispressed out of the pump chamber 13 when its volume decreases, i.e. atthe location of a so-called high pressure pump section H.

FIG. 3 is a tangential cross section of an embodiment of the roller vanepump according to the invention. In this figure similar pump parts areprovided with the same reference numeral as provided in FIGS. 1 and 2.On either axial side of the carrier 4, there is provided a bearing bush30 in the pump housing 12 through which the pump shaft 5 extends in theaxial direction. The bearing bushes 30 provide a bearing surface for therotation of the pump shaft 5 and also stiffen the construction of thepump. At an axial end 33 of the bearing bush 30 closest to the carrier4, the bushes 30 are provided with a hook part 38 that is formed by aradially outwardly oriented thickening that interacts with the pumphousing 12 to prevent the bushes 30 from axially moving with respect tothe pump housing 12. Lubrication fluid is provided to a gap (not shown)between the radially inner surface of the bushes 30 and the radiallyouter surface of the pump shaft 5 from an essentially annular cavity 39within the pump housing 12. Here said cavity 39 is bound by the carrier4, the pump shaft 5 and the bearing bush 30. In the cavity 39 thereexists an elevated fluid pressure as a result of a leakage flow from thepump chambers 13, in particular the chambers 13 at the location of ahigh pressure pump section H, to the cavity 39. This leakage is enabledby a small gap (not shown) between the housing 12 and the carrier 4,which gap allows the carrier 4 to rotate in the housing 12. The annularcavity 39 advantageously forms a reservoir for lubrication fluid at anelevated pressure, from which cavity 39 the interface between the pumpshaft 5 and the bushes 30 is reliably provided with lubrication.

FIGS. 4 and 5 are two views of an embodiment of the bearing bush 30,whereby FIG. 4 is a perspective view and FIG. 5 is a plane view of aradially inner surface of the bush 30. In FIG. 4 the dashed linesschematically indicate the outer edges of the corner 4 and the shaft 5.In the embodiment of FIGS. 4 and 5, the bearing bush 30 is provided witha lubrication groove 31 on its radially inner surface having asubstantially elongated shape with a long axis 32, whereby thelubrication groove 31 starts at an axial end 33 of the bearing bush 30closest to the carrier 4 and continues with its long axis 32 oriented atan angle of about 60 degrees with the axial direction, such that itextends in tangential direction in the direction of rotation 50 of thepump shaft. The lubrication groove 31 allows a flow of lubrication fluidin between the pump shaft 5 and the bearing bush, even when the bearingbush 30 fits relatively tightly around said shaft 5. To preventsubstantial fluid communication with the environment, the lubricationgroove 30 ends at some distance from an axial end 34 of the bearing bushopposite the said axial end 33 of the bearing bush 30 closest to thecarrier 4. As indicated in FIG. 5 the bearing bush 30 is oriented suchthat it starts at a tangential position of a discharge section H1 of thepump where the prevailing pressure is at a maximum and it continues intangential direction through a suction section L up to the tangentialposition of a discharge section H2 where the prevailing pressure issmaller than it the first mentioned section H1, so that it extends intangential direction of an angle of about π minus ½π divided by 2, i.e.the number of pump units of the pump of FIG. 3.

According to the invention the bearing bush 30 may be provided with afurther lubrication groove 35, as is indicated by the dashed lines inFIG. 5. It is further advantageous to provide the radially inner surfaceof the bearing bush 30 with a distribution groove 36 having a long axis37 that is oriented substantially axially and intersecting the long axis32 of the lubrication groove 31. The distribution groove 36 extends overa distance of at about ½ of an axial dimension of the bush 30, butremains at a distance of about ¼ from either axial end 33, 34 thereof tolimit communication of lubrication fluid between the distribution groove36 and the environment.

The continuously variable transmission 63 shown in FIG. 6 is providedwith an input shaft 61 to be drivably connected to an engine 60, anoutput shaft 62 to be drivingly connected to a load and provided with aroller vane pump 12 as described here above, wherein the pump shaft 5 isdrivably connected to the engine 60.

What is claimed is:
 1. A roller vane pump provided with a pump housingaccommodating a substantially cylindrical carrier, which is rotatableabout a central axis, and a cam ring encompassing the carrier in theradial direction, and with a pump shaft extending co-axial with saidcentral axis through the carrier, wherein there is provided in the pumphousing a bearing bush having an essentially cylindrical central borethrough which the pump shaft extends, which bearing bush is providedwith a lubrication groove on a radially inner surface thereof forallowing fluid to penetrate between the bearing bush and the pump shaft,wherein the lubrication groove starts at a tangential position on theradially inner surface of the bearing bush corresponding to a tangentialposition of a discharge section of the roller vane pump.
 2. Roller vanepump according to claim 1, wherein, when the pump is provided with morethan one discharge section, the lubrication groove starts at atangential position on the radially inner surface of the bearing bushcorresponding to a tangential position of a discharge section of theroller vane pump where a prevailing fluid pressure is at a maximumduring operation of the pump.
 3. Roller vane pump according to claim 1,wherein the bearing bush is made of copper or of a copper alloy. 4.Roller vane pump according to claim 1, wherein the pump housing ispredominantly made of aluminium.
 5. Roller vane pump according to claim1, wherein there is provided in the pump housing a further bearing bush,whereby the beating bush and the further bearing bush are each providedon axially opposite sides of the carrier.
 6. Roller vane pump accordingto claim 1, wherein the bearing bush is provided with a hook part formedby a radially outwardly oriented thickening that interacts with the pumphousing to prevent axial movement of the bearing bush with respect tothe pump housing.
 7. Roller vane pump according to claim 1, whereinthere is provided a cavity that is in communication with a pump chamberthrough a gap between the carrier and the pump housing and with a gapbetween the bearing bush and the pump shaft.
 8. A continuously variabletransmission provided with an input shaft to be drivably connected to anengine, an output shaft to be drivingly connected to a load and providedwith a roller vane pump according to claim 1, wherein the pump shaft isdrivably connected to the engine.
 9. Roller vane pump according to claim1, wherein the lubrication groove has a substantially elongated shapehaving a long axis, whereby the lubrication groove starts at an axialend of the bearing bush closest to the carrier and continues in adirection having at least an axial component.
 10. Roller vane pumpaccording to claim 9, wherein the lubrication groove is predominantlylocated in a region of tangential positions on the radially innersurface of the bearing bush where a contact pressure between the pumpshaft and bearing bush is relatively low, at least during operation ofthe pump.
 11. Roller vane pump according to claim 1, wherein thelubrication groove tangentially extends from the said tangentialposition in a direction of rotation of the pump shaft.
 12. Roller vanepump according to claim 11, wherein the bearing bush is provided with afurther lubrication groove on its radially inner surface, which furtherlubrication groove starts at an axial end of the bearing bush closest tothe carrier and continues in a direction having an axial component,whereby the further lubrication groove tangentially extends opposite thedirection of rotation of the pump shaft.
 13. Roller vane pump accordingto claim 1, wherein the lubrication groove is dimensioned such that ittangentially extends over an angle that approximately corresponds to πminus ½π divided by the number of pump units of the pump.
 14. Rollervane pump according to claim 13, wherein the bearing bush is providedwith a further lubrication groove on its radially inner surface, whichfurther lubrication groove starts at an axial end of the bearing bushclosest to the carrier and continues in a direction having an axialcomponent, whereby the further lubrication groove tangentially extendsopposite the direction of rotation of the pump shaft.
 15. Roller vanepump according to claim 1, wherein the bearing bush is provided with adistribution groove on its radially inner surface, which distributiongroove has a substantially elongated shape having a long axis that issubstantially axially oriented and that intersects the long axis of thelubrication groove.
 16. Roller vane pump according to claim 15, whereinthe distribution groove is dimensioned such that there remains an axialdistance between the distribution groove and either axial end of thebearing bush of at least ¼ of an axial dimension of the bearing bush.17. A roller vane pump provided with a pump housing accommodating asubstantially cylindrical carrier, which is rotatable about a centralaxis, and a cam ring encompassing the carrier in the radial direction,and with a pump shaft extending co-axial with said central axis throughthe carrier, wherein there is provided in the pump housing a bearingbush having an essentially cylindrical central bore through which thepump shaft extends, which bearing bush is provided with a lubricationgroove on a radially inner surface thereof for allowing fluid topenetrate between the bearing bush and the pump shaft, wherein thelubrication groove starts at a tangential position on the radially innersurface of the bearing bush corresponding to a tangential position of adischarge section of the roller vane pump and at an axial end of thebearing bush closest to the carrier and ends at some distance from anaxial end of the bearing bush opposite the said axial end closest to thecarrier.